Magnetic ferrite composition and process of production thereof

ABSTRACT

A magnetic ferrite composition including at least one of Mg, Ni, Cu, Zn, Mn, and Li and having a content of carbon within a predetermined range, for example, over 9.7 weight ppm to less than 96 weight ppm. The composition may be used as the magnetic core for an inductor, transformer, coil, etc. used for radios, televisions, communication devices, office automation equipment, switching power sources, and other electronic apparatuses or magnetic heads for video apparatuses or magnetic disk drives or other electronic components.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a ferrite composition and aprocess of production thereof.

[0003] 2. Description of the Related Art

[0004] Mn—Zn ferrite components, Ni—Cu—Zn ferrite components, Mn—Mg—Znferrite components, and other magnetic ferrite compositions are madebroad use of for various types of electronic apparatuses as for examplemagnetic cores for coils, transformers, magnetic heads, etc.

[0005] Along with the recent reduction in size and reduction inthickness of electronic apparatuses, a similar reduction in size andreduction in thickness of the magnetic ferrite components have becomedesirable. In order to maintain the reliability of the product alongwith this, a higher mechanical strength and higher magneticcharacteristics are demanded.

[0006] From this viewpoint, to improve the mechanical strength, thereare known the methods of using a hot press for manufacture, reducing theparticle diameter of the raw material powder and lowering the sinteringtemperature to reduce the crystal particle diameter, or adding varioustypes of additives to reduce the crystal particle diameter. Further, toimprove the magnetic characteristics, there are known the methods ofadding various types of additives and optimizing the sinteringconditions.

[0007] With the method of using a hot press to improve the mechanicalstrength, however, the production time becomes longer and expensiveequipment is required, so there are large cost demerits.

[0008] Further, with the method of making the raw material powder finerto improve the mechanical strength, a separate process for reducing theparticle diameter becomes necessary. Also, the finer raw material powderis extremely difficult to handle when producing a magnetic ferritecomponent.

[0009] Further, with the method of improving the mechanicalcharacteristics by adding various types of additives, there are largecost demerits and balancing the various magnetic characteristics becomesdifficult in some cases.

[0010] Still further, with the method of improving the magneticcharacteristics by optimizing the sintering conditions, control of thesintering atmosphere, temperature raising and lowering rate, etc.becomes difficult, introduction of new equipment becomes necessary insome cases, and other problems arise.

[0011] Note that Japanese Unexamined Patent Publication (Kokai) No.1994-132111 discloses the amount of carbon contained in a ferritesintered body, but makes no mention at all of the control of the same.Further, the actually included amount of carbon is normally about thesame extent as the amount of carbon included in a sintered body obtainedby removing the binder and then sintering (about 100 ppm) and it isdifficult to secure sufficient mechanical strength. That is, in theabove publication, the raw material powder is compacted by coldisostatic pressing and sintered in the state with difficult release ofoxygen when the hematite material changes to spinel type ferrite.Therefore, the carbon added to the raw material powder before sinteringor the reducing agent breaking down under heating to become carbon hasan effect on the magnetic characteristics of the phase after sintering.Further, the above publication makes no mention at all of the effect ofthe residual carbon on the strength and magnetic characteristics.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to solve the above problemsin the related art and provide a ferrite composition having a highmechanical strength and superior magnetic characteristics even whenreducing the size and reducing the thickness and a process forproduction of the same.

[0013] The present inventors took note of the content of carbon in amagnetic ferrite composition and controlled the same to thereby perfectthe present invention. Note that in the present invention, a “magneticferrite composition” is used in the sense including both a ferritematerial and ferrite sintered body.

[0014] The magnetic ferrite composition according to the presentinvention is characterized by including at least one of Mg, Ni, Cu, Zn,Mn, and Li and having a content of carbon of less than 96 weight ppm,preferably not more than 91 weight ppm, more preferably not more than 77weight ppm, particularly preferably not more than 70 weight ppm.

[0015] The ferrite composition preferably includes, in addition to Mg,at least one of Cu, Zn, Mn, Ni, and Li. A typical example of thisferrite composition is Mg—Cu—Zn ferrite. In such a ferrite composition,the content of the carbon is preferably over 9.7 weight ppm (more than9.7 weight ppm), more preferably at least 10 weight ppm, particularlypreferably at least 15 weight ppm. Further, in such a ferritecomposition, the content of carbon is preferably not more than 91 weightppm.

[0016] The ferrite composition may be a ferrite composition including atleast Mn and Zn. A typical example of such a ferrite composition is anMn—Zn ferrite composition. In such a ferrite composition, the content ofcarbon is less than 52 weight ppm, preferably not more than 50 weightppm, more preferably not more than 45 weight ppm. Further, in such aferrite composition, the content of carbon is preferably over 9.8 weightppm (more than 9.8 weight ppm), more preferably at least 10 weight ppm,particularly preferably at least 15 weight ppm.

[0017] The ferrite composition may further include as an additionalcomponent at least one oxide selected from silicon oxide, calcium oxide,tin oxide, titanium oxide, niobium oxide, zirconium oxide, vanadiumoxide, molybdenum oxide, bismuth oxide, and tantalum oxide.

[0018] Further, the ferrite composition may be a ferrite compositionincluding at least one of Cu, Zn, and Mn in addition to Ni. A typicalexample of such a ferrite composition is an Ni—Cu—Zn ferritecomposition. In such a ferrite composition, the content of carbon isless than 67 weight ppm, preferably not more than 60 weight ppm, morepreferably not more than 50 weight ppm, particularly preferably not morethan 45 weight ppm. Further, in such a ferrite composition, the contentof carbon is preferably over 9.7 weight ppm (more than 9.7 weight ppm),more preferably at least 10 weight ppm, particularly preferably at least15 weight ppm.

[0019] The process of production of a magnetic ferrite compositionaccording to the present invention controls a flow rate of gas blowninto the sintering furnace so as to control the amount of carboncontained in the ferrite composition.

[0020] Further, the method of adjusting the bending strength of themagnetic ferrite composition according to the present invention controlsthe content of the carbon contained in the magnetic ferrite composition.

[0021] In the present invention, by controlling the content of thecarbon in the magnetic ferrite composition, it is possible to improvethe mechanical strength of the magnetic ferrite composition (forexample, to give a bending strength of preferably at least 8 kgf/mm²,more preferably at least 10 kgf/mm²) and to provide a highly reliableferrite composition with little cracking or chipping.

[0022] In the present invention, by controlling the content of thecarbon in the magnetic ferrite composition to within a predeterminedrange, it is possible to improve the bending strength while maintaininga high magnetic permeability μ in a magnetic ferrite composition of apredetermined composition. Further, in a magnetic ferrite composition ofanother composition, it is possible to improve the bending strengthwhile maintaining a low core loss.

[0023] Note that the carbon contained in the ferrite composition aftersintering is considered to be the carbon component contained in thecarbonate material and/or organic binder.

[0024] The ferrite composition according to the present invention may beused as the core of an inductor, transformer, coil, etc. used in anelectronic apparatus such as a radio, television, communicationsapparatus, office automation apparatus, and switching power source or amagnetic head core used in an electronic apparatus such as a videoapparatus or magnetic disk drive or other electronic components.

[0025] Among these, the Mg—Cu—Zn ferrite composition and Ni—Cu—Znferrite composition according to the present invention may be preferablyused for inductors, while the Mn—Zn ferrite composition may bepreferably used for transformers.

[0026] In the process of production of a ferrite composition accordingto the present invention, when producing the ferrite sintered body, itis possible to blow a gas into the sintering furnace at the time ofsintering by a predetermined flow rate and skip the carbon componentincluded in the granulated material to control the amount of carbonafter sintering. Therefore, it is easy to balance the mechanicalstrength and the magnetic characteristics of the obtained ferritesintered body.

[0027] The method of adjusting the bending strength of the ferritesintered body according to the present invention can control the bendingstrength of the ferrite sintered body obtained by controlling the amountof carbon in the composition. This new discovery was made by the presentinventors.

[0028] The present disclosure relates to subject matter contained inJapanese Patent Application No. 1999-264775, filed on September 20, thedisclosure of which is expressly incorporated herein by reference in itsentirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] These and other objects and features of the present inventionwill become clearer from the following description of the preferredembodiments given with reference to the attached drawings, in which:

[0030]FIG. 1 is a graph of the relationship between the amount of carbonand magnetic permeability of the ferrite sintered bodies of Examples 1to 7, Reference Example 1, and Comparative Example 1;

[0031]FIG. 2 is a graph of the relationship between the amount of carbonand bending strength of the ferrite sintered bodies of Examples 1 to 7,Reference Example 1, and Comparative Example 1;

[0032]FIG. 3 is a graph of the relationship between the amount of carbonand core loss of the ferrite sintered bodies of Examples 8 to 11,Reference Example 2, and Reference Example 3;

[0033]FIG. 4 is a graph of the relationship between the amount of carbonand bending strength of the ferrite sintered bodies of Examples 8 to 11,Reference Example 2, and Reference Example 3;

[0034]FIG. 5 is a graph of the relationship between the amount of carbonand magnetic permeability of the ferrite sintered bodies of Examples 12to 16, Reference Example 4, and Reference Example 5; and

[0035]FIG. 6 is a graph of the relationship between the amount of carbonand bending strength of the ferrite sintered bodies of Examples 12 to16, Reference Example 4, and Reference Example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] First Embodiment

[0037] The ferrite sintered body according to the first embodiment canbe produced for example as follows.

[0038] First, the starting materials are weighed and mixed so as to givethe predetermined ratio of composition and obtain the raw materialmixture.

[0039] The weighing is normally performed at an accuracy of 1/1000. Asthe method of mixing, for example, wet mixing using a ball mill and drymixing using a dry mixer may be mentioned. Note that the averageparticle diameter of the starting material is preferably 0.1 to 3 μm.

[0040] The raw material mixture in the present embodiment contains, inaddition to the iron oxide or material becoming iron oxide aftersintering, at least one oxide selected from magnesium oxide, nickeloxide, copper oxide, zinc oxide, manganese oxide, lithium oxide, ormaterials becoming these metal oxides after sintering. Note thatmaterials becoming metal oxides after sintering include metals alone,carbonates, hydroxides, halides, etc.

[0041] The composition of the ferrite composition of the presentembodiment is not particularly limited. Various compositions may beselected in accordance with the objective, but it is preferable that thecomposition contain as main ingredients Fe₂O₃ and at least one oxideselected from the group of MgO, CuO, ZnO, MnO, NiO, and Li₂O. A typicalexample of the ferrite composition of the present embodiment is anMg—Cu—Zn ferrite composition.

[0042] The raw material mixture in the present embodiment may also havevarious types of additives added to it in addition to the above mainingredients.

[0043] Note that the raw material mixture in the present embodiment maycontain impurity elements in the material. As such elements, B, Al, Si,P, Ca, Cr, Co, Na, K, S, Cl, etc. may be mentioned. To keep down thepower loss or effect on the magnetic characteristics, it is preferablethat the ratio by weight of these elements with respect to thecomposition as a whole be not more than 200 ppm, but P and B have alarge effect on the power loss or magnetic characteristics, so the ratioby weight of P with respect to the composition as a whole is preferably0 to 30 ppm or the ratio by weight of B with respect to the compositionas a whole is preferably 0 to 50 ppm.

[0044] Next, the raw material mixture is prefired to obtain a prefiredmaterial. The prefiring is performed to break down the materials byheat, homogenize the components, produce ferrite, eliminate ultra-fineparticles due to sintering and grow the particle diameter to a suitablesize of the particles, and convert the raw material mixture to a formsuited for post processing. This prefiring is preferably performed at atemperature of 700 to 1000° C. normally for one to three hours. Theprefiring may be performed in the air or in an atmosphere having ahigher oxygen partial pressure than air or a pure oxygen atmosphere.Note that when including additional ingredients in the ferritecomposition, the main ingredients and additional ingredients may bemixed before the prefiring or after the prefiring.

[0045] Next, the prefired material is pulverized to obtain a pulverizedmaterial. The pulverization is performed to break up aggregates of theprefired material to produce a powder having a suitable sinterability.When the prefired material forms large masses, the material is roughlypulverized then wet pulverized using a ball mill or attritor mill etc.The wet pulverization is performed until the average particle diameterof the prefired material becomes preferably 1 to 2 μm.

[0046] Next, the pulverized material is granulated to obtain agranulated material. The granulation is performed to make the pulverizedmaterial into aggregated particles of a suitable size to convert it to aform suitable for shaping. As this granulation method, for example, thepress granulation method or spray dry method etc. may be mentioned. Inthe present embodiment, the spray dry method is used of adding polyvinylalcohol or another ordinarily used binder to the pulverized material,then atomizing it in a spray dryer and drying it at a low temperature.

[0047] Next, the granulated material is shaped to a predetermined shapeto obtain a shaped article. As the shaping of the granulated material,for example, dry shaping, wet shaping, extrusion, etc. may be mentioned,but in the present embodiment, the dry shaping method of filling thegranulated material into a mold and then pressing it is used. The shapeof the shaped article is not particularly limited, but for example atoroidal shape etc. may be mentioned.

[0048] Next, the shaped article is sintered to obtain a ferrite sinteredbody of the composition according to the present embodiment. Thesintering is performed to cause the powder particles of the shapedarticle including the large number of voids to become cohesive at atemperature under the melting point to obtain a dense sintered body. Asthe furnace used for the sintering, one of the batch type, pusher type,cart type, etc. may be mentioned.

[0049] In the present embodiment, for example air or another gas isblown into the furnace during sintering by a flow rate of preferablymore than 25 ml/min to less than 5000 ml/min, more preferably 200 to4000 ml/min.

[0050] If the flow rate of gas blown into the furnace is too small, theamount of carbon contained after sintering tends to become large and themechanical strength of the ferrite sintered body obtained to become low.Further, if the flow rate of the gas blown into the furnace is toolarge, the amount of carbon contained after sintering tends to becometoo small and the magnetic permeability of the obtained ferrite sinteredbody to become low. That is, by sintering while blowing gas into thefurnace by a predetermined flow rate, it is possible to control theamount of carbon contained after sintering and balance the mechanicalstrength (bending strength) and magnetic characteristics (magneticpermeability) of the obtained ferrite sintered body.

[0051] The sintering temperature is preferably 900 to 1300° C. If thesintering temperature is too low, not only does the sintering tend tobecome insufficient, but also the amount of carbon contained aftersintering tends to become larger. The sintering time is normally about 1to 3 hours. The sintering may be performed in the air or in anatmosphere with an oxygen partial pressure higher than air.

[0052] By going through the above process, a ferrite sintered bodycontrolled in amount of carbon to a suitable value is obtained.

[0053] The average crystal particle diameter of the ferrite sinteredbody is preferably 1 to 30 μm. If the average crystal particle diameteris too small, the hysteresis loss tends to become large, while if theaverage crystal particle diameter is too large, the eddy current losstends to become large.

[0054] The ferrite sintered body of the composition according to thepresent embodiment can be improved in mechanical strength whilemaintaining a high magnetic permeability by controlling the content ofcarbon to within a predetermined range (over 9.7 weight ppm to less than96 weight ppm). Further, according to the process of the presentembodiment, the content of the carbon is controlled by sintering whileblowing gas by a predetermined flow rate into the furnace, so it ispossible to produce a ferrite sintered body controlled in amount ofcarbon after sintering to a suitable amount simply and inexpensively.Accordingly, by using this ferrite sintered body to construct aninductor magnetic core, it is possible to obtain a product superior inmagnetic permeability, prevented from cracking or chipping even if thin,and superior in reliability. Further, this contributes to the reductionof size and reduction of cost of the product.

[0055] Second Embodiment

[0056] The ferrite sintered body according to the second embodiment maybe produced for example in the following way.

[0057] In the same way as the first embodiment, first, the startingmaterials are weighed and mixed to a predetermined ratio of compositionto obtain a raw material mixture. Note that the average particlediameter of the starting materials is preferably 0.1 to 3 μm.

[0058] The composition of the ferrite composition is not particularlylimited. Various compositions may be selected in accordance with theobjective. Preferably, the ferrite composition contains, in addition toFe₂O₃, MnO and ZnO. A typical example of the ferrite composition of thepresent embodiment is an Mn—Zn ferrite composition.

[0059] In this case, the raw material mixture contains as mainingredients iron oxide, manganese oxide, and zinc oxide or materialsbecoming these metal oxides after sintering. Note that materialsbecoming metal oxides after sintering include metals alone, carbonates,hydroxides, halides, etc.

[0060] The raw material mixture in the present embodiment preferably hasthe following additional ingredients added to it in addition to theabove main ingredients.

[0061] The additional ingredients include at least one oxide selectedfrom silicon oxide, calcium oxide, tin oxide, titanium oxide, niobiumoxide, zirconium oxide, vanadium oxide, molybdenum oxide, bismuth oxide,and tantalum oxide.

[0062] Preferably, the additional ingredients include at least one oxideselected from silicon oxide in an amount of addition converted to SiO₂of 50 to 2000 ppm, calcium oxide in an amount of addition converted toCaO of 100 to 3100 ppm, tin oxide in an amount of addition converted toSnO₂ of not more than 8500 ppm (not including 0), titanium oxide in anamount of addition converted to TiO₂ of not more than 12000 ppm (notincluding 0), niobium oxide in an amount of addition converted to Nb₂O₅of 50 to 300 ppm, zirconium oxide in an amount of addition converted toZrO₂ of 200 to 1200 ppm, vanadium oxide in an amount of additionconverted to V₂O₅ of 100 to 1100 ppm, molybdenum oxide in an amount ofaddition converted to MoO₃ of 50 to 310 ppm, bismuth oxide in an amountof addition converted to Bi₂O₃ of 350 to 800 ppm, and tantalum oxide inan amount of addition converted to Ta₂O₅ of 400 to 1400 ppm. By addingthese additional ingredients in this range, the Br (residual magneticflux density) is reduced, the ΔB (=Bm-Br) increases, the power lossdecreases, and the magnetic characteristics are improved.

[0063] Note that the raw material mixture in the present embodiment mayinclude impurity elements in the materials. As such elements, B, Al, P,Cr, Co, Na, K, S, Cl, etc. may be mentioned. To keep down the power lossand the effect on the magnetic characteristics, the ratio by weight ofeach element with respect to the composition as a whole is preferablynot more than 200 ppm, but P and B have a large effect on the power lossor magnetic characteristics, so the ratio by weight of P with respect tothe composition as a whole is preferably 0 to 30 ppm or the ratio byweight of B with respect to the composition as a whole is preferably 0to 50 ppm.

[0064] Next, the raw material mixture is prefired, pulverized,granulated, and shaped, then sintered to obtain a ferrite shaped articlein the same way as in the first embodiment. Further, in the presentembodiment, an atmospheric gas preferably substantially the same as thesintering atmosphere is blown into the furnace during sintering at aflow rate of preferably more than 100 ml/min and less than 5000 ml/min,more preferably 300 to 4000 ml/min. If the flow rate of the atmosphericgas blown into the furnace is too small, the amount of carbon containedafter sintering tends to become large, the mechanical strength of theferrite sintered body obtained to become low, and further the core lossto increase. Further, if the flow rate of the atmospheric gas blown intothe furnace is too large, the amount of carbon contained after sinteringtends to become too small and the core loss of the obtained ferritesintered body to become high. That is, by sintering while blowingatmospheric gas into the furnace by a predetermined flow rate, it ispossible to control the content of carbon after sintering and possibleto balance the mechanical strength (bending strength) and magneticcharacteristics (core loss) of the ferrite sintered body obtained.

[0065] The sintering temperature is preferably 1200 to 1400° C. If thesintering temperature is too low, not only does the sintering tend tobecome insufficient, but also the amount of carbon contained aftersintering tends to become larger. The sintering time is normally about 3to 7 hours.

[0066] By going through the above process, a ferrite sintered bodycontrolled in amount of carbon to a suitable value is obtained.

[0067] The average crystal particle diameter of the ferrite sinteredbody is preferably 1 to 30 μm. If the average crystal particle diameteris too small, the hysteresis loss tends to become large, while if theaverage crystal particle diameter is too large, the eddy current losstends to become large.

[0068] The ferrite sintered body of the composition according to thepresent embodiment can be improved in mechanical strength while reducingthe core loss by controlling the content of carbon to within apredetermined range (over 9.8 weight ppm to less than 52 weight ppm).Further, according to the process of the present embodiment, the contentof the carbon is controlled by sintering while blowing gas by apredetermined flow rate into the furnace, so it is possible to produce aferrite sintered body controlled in amount of carbon after sintering toa suitable amount simply and inexpensively. Accordingly, by using thisferrite sintered body to construct a transformer magnetic core, it ispossible to obtain a product with a small core loss, prevented fromcracking or chipping even if thin, and superior in reliability. Further,this contributes to the reduction of size and reduction of cost of theproduct.

[0069] Third Embodiment

[0070] The ferrite sintered body according to the third embodiment maybe produced for example in the following way.

[0071] In the same way as the first and second embodiments, first, thestarting materials are weighed and mixed to a predetermined ratio ofcomposition to obtain a raw material mixture. Note that the averageparticle diameter of the starting materials is preferably 0.1 to 3 μm.

[0072] The raw material mixture in the present embodiment contains, inaddition to the iron oxide and nickel oxide or material becoming theseoxides after sintering, at least one oxide selected from copper oxide,zinc oxide, and manganese oxide or materials becoming these metal oxidesafter sintering. Note that materials becoming metal oxides aftersintering include metals alone, carbonates, hydroxides, halides, etc.

[0073] The composition of the ferrite composition is not particularlylimited. Various compositions may be selected in accordance with theobjective. Preferably, the composition contains as main ingredientsFe₂O₃, NiO, and at least one oxide selected from CuO, ZnO, and MnO. Atypical example of the ferrite composition of the present embodiment isan Ni—Cu—Zn ferrite composition.

[0074] The raw material mixture in the present embodiment may have addedto it various types of additives in addition to the above mainingredients.

[0075] Note that the raw material mixture in the present embodiment mayinclude impurity elements in the materials. As such elements, B, Al, Si,P, Ca, Cr, Co, Na, K, S, Cl, etc. may be mentioned. To keep down thepower loss and the effect on the magnetic characteristics, the ratio byweight of each element with respect to the composition as a whole ispreferably not more than 200 ppm, but P and B have a large effect on thepower loss or magnetic characteristics, so the ratio by weight of P withrespect to the composition as a whole is preferably 0 to 30 ppm or theratio by weight of B with respect to the composition as a whole ispreferably 0 to 50 ppm.

[0076] Next, the raw material mixture is prefired, pulverized,granulated, and shaped, then sintered to obtain a ferrite shaped articlein the same way as in the first embodiment.

[0077] In the present embodiment, for example air or another gas isblown into the furnace during sintering by a flow rate of preferablymore than 100 ml/min and less than 5000 ml/min, more preferably 200 to4000 ml/min. If the flow rate of the gas blown into the furnace is toosmall, the content of the carbon after sintering becomes larger and themechanical strength of the ferrite sintered body obtained ends to becomelow. Further, if the flow rate of gas blown into the furnace becomes toolarge, the content of carbon after sintering tends to become too smalland the magnetic permeability of the ferrite sintered body obtained tobecome low. That is, by sintering the material while blowing gas intothe furnace by a predetermined flow rate, it is possible to control theamount of carbon after sintering and possible to balance the mechanicalstrength (bending strength) and magnetic characteristics (magneticpermeability) of the ferrite sintered body obtained. Note that thesintering temperature, sintering time, and sintering atmosphere may bemade the same as in the first embodiment.

[0078] By going through the above process, a ferrite sintered bodycontrolled in amount of carbon to a suitable value is obtained.

[0079] The average crystal particle diameter of the ferrite sinteredbody is preferably 1 to 30 μm. If the average crystal particle diameteris too small, the hysteresis loss tends to become large, while if theaverage crystal particle diameter is too large, the eddy current losstends to become large.

[0080] The ferrite sintered body of the composition according to thepresent embodiment can be improved in mechanical strength whilemaintaining a high magnetic permeability by controlling the amount ofcarbon to within a predetermined range (over 9.7 weight ppm to less than60 weight ppm). Further, according to the process of the presentembodiment, the content of the carbon is controlled by sintering whileblowing gas by a predetermined flow rate into the furnace, so it ispossible to produce a ferrite sintered body controlled in amount ofcarbon after sintering to a suitable amount simply and inexpensively.Accordingly, by using this ferrite sintered body to construct aninductor magnetic core, it is possible to obtain a product superior inmagnetic permeability, prevented from cracking or chipping even if thin,and superior in reliability. Further, this contributes to the reductionof size and reduction of cost of the product.

[0081] Next, the present invention will be explained in further detailby more specific examples, but the present invention is not limited tothese examples.

EXAMPLES 1 to 7, REFERENCE EXAMPLE 1, COMPARATIVE EXAMPLE 1

[0082] As the materials, 48.0 mol % of Fe₂O₃, 19.3 mol % of MgO, 7.1 mol% of CuO, and 25.6 mol % of ZnO were weighed, then wet mixed by a ballmill for 16 hours to obtain a raw material mixture.

[0083] Next, the raw material mixture was prefired at 900° C. for 2hours to obtain a prefired material, then was wet pulverized by a ballmill for 16 hours to obtain a pulverized material.

[0084] Next, 10 wt % of an 6% aqueous solution of polyvinyl alcohol wasadded as a binder to 100 wt % of the pulverized material and granulatedto obtain a granulated material. This was pressed at a pressure of 1ton/cm² to a toroidal shape to obtain a shaped article. Further, for thetest of the bending strength, the material was pressed at a pressure of1 ton/cm² to a rod shape of 5×5×500 mm to obtain a shaped article.

[0085] Next, these shaped articles were placed in a sintering furnacefor sintering. This sintering was performed by blowing air inside thefurnace while changing the flow rate of blowing as shown in Table 1(unit:ml/min) in an air atmosphere at a sintering temperature of 1020°C. for a sintering time of 2 hours to obtain ferrite sintered bodies.

[0086] The amount of carbon of each ferrite sintered body obtained inthis way (unit:ppm) was measured. The amount of carbon was measuredusing a carbon-sulfur analyzer (EMIA520) made by Horiba Seisakusho,sintering the sample by high frequency heating in a flow of oxygen, andmeasuring by the infrared absorption method. The results are shown inTable 1.

[0087] Further, the magnetic permeability μ of each obtained ferritesintered body was measured. The magnetic permeability μ was found bywinding a copper wire (wire diameter:0.35 mm) around a sample 20 turns,measuring the inductance at a measurement frequency of 100 kHz andmeasurement current of 0.25 mA by an LCR meter (made byHewlett-Packard), and calculating using the following equation (1). Theresults are shown in Table 1. The relationship with the amount of carbonis shown in FIG. 1.

Magnetic permeability μ=(le×L)(μ₀ ×Ae×N ²)   (1)

[0088] Here, le is the length of the magnetic path, L is the inductanceof the sample, μ₀ is the magnetic permeability in vacuum=4n×10⁻⁷ (H/m),Ae is the sectional area of the sample, and N is the number of turns ofthe coil.

[0089] Further, the bending strength was tested in accordance withJIS-R1601 using a rod-shaped ferrite sintered body. The results areshown in Table 1. The relationship with the amount of carbon is shown inFIG. 2. TABLE 1 Gas flow Am't of Bending Magnetic rate carbon strengthpermeability (ml/min) (ppm) (kgf/mm²) μ Comp. 25 96 7.8 852 Ex. 1 Ex. 1.50 91 8 845 Ex. 2 100 77 10 833 Ex. 3 200 67 10.4 821 Ex. 4 300 55 12.3812 Ex. 5 500 48 13.4 802 Ex. 6 1000 41 14.5 782 Ex. 7 3000 33 14.6 772Ref. 5000 9.7 16.5 734 Ex. 1

[0090] From the above results, it was confirmed that if the amount ofthe carbon after sintering is 96 ppm (Comparative Example 1), thebending strength is a low 7.8 kgf/mm² and the ferrite shaped articlelacks reliability.

[0091] As opposed to this, when the amount of carbon after sintering isnot more than 91 ppm (Examples 1 to 7 and Reference Example 1), thebending strength is a sufficiently large 8 kgf/mm² to 16.5 kgf/mm² andthe magnetic permeability μ is a sufficiently large 734 to 845. Amongthese, Examples 2 to 7 were well balanced in bending strength andmagnetic permeability. Note that it was confirmed that when the amountof carbon after sintering is 9.7 ppm (Reference Example 1), while themagnetic permeability tends to fall somewhat, there is not that much ofa problem in practice.

EXAMPLES 8 to 11, REFERENCE EXAMPLE 2, and REFERENCE EXAMPLE 3

[0092]53.6 mol % of Fe₂O₃, 36.2 mol % of MnO, and 10.2 mol % of ZnO wereweighed, then wet mixed by a ball mill for 16 hours to obtain a rawmaterial mixture.

[0093] Next, the raw material mixture was prefired at 850° C. to obtaina prefired material, then 110 weight ppm of SiO₂ powder, 500 weight ppmof CaO powder, 3300 weight ppm of SnO₂ powder, 320 weight ppm of Nb₂O₅powder, and 100 weight ppm of MoO₃ powder were added to 100 wt % of sucha prefired material, then the results were wet pulverized by a ball millfor three hours to obtain a pulverized material.

[0094] Next, 10 wt % of an 8% aqueous solution of polyvinyl alcohol wasadded as a binder to 100 wt % of the pulverized material and the resultgranulated to obtain a granulated material. This was pressed in the sameway as in Examples 1 to 7 to obtain a toroidal shaped article androd-shaped article.

[0095] Next, these shaped articles were placed in a sintering furnacefor sintering. This sintering was performed by blowing a sinteringatmosphere gas controlled in oxygen partial pressure inside the furnacewhile changing the flow rate of blowing as shown in Table 2(unit:ml/min) in an atmosphere controlled in oxygen partial pressure ata sintering temperature of 1300° C. for a sintering time of 5 hours toobtain ferrite sintered bodies.

[0096] The amounts of carbon of the obtained ferrite sintered bodieswere measured in the same way as in Examples 1 to 7. The results areshown in Table 2.

[0097] Further, a sine wave alternating current magnetic field of 100kHz and 200 mT was applied to the obtained ferrite sintered body basedon JIS-C2561-1992 and the core loss at 100° C. (unit:kW/m³) wasmeasured. The results are shown in Table 2. The relationship with theamount of carbon is shown in FIG. 3.

[0098] Further, the same procedure was followed as in Examples 1 to 7 totest the bending strength using the rod shaped ferrite sintered body.The results are shown in Table 2. The relationship with the amount ofcarbon is shown in FIG. 4. TABLE 2 Gas flow Am't of Bending Core ratecarbon strength loss (ml/min) (ppm) (kgf/mm²) (kW/m³) Ref. 100 52 5.7530 Ex. 2 Ex. 8 300 42 9.7 407 Ex. 9 500 35 10.4 368 Ex. 10 1000 30 14.4374 Ex. 11 3000 18.6 16.6 433 Ref. 5000 9.8 20.2 506 Ex. 3

[0099] From the above results, it was confirmed that when the amount ofcarbon after sintering is 52 ppm (Reference Example 2), the bendingstrength is a relatively low 5.7 kgf/mm².

[0100] As opposed to this, when the amount of carbon after sintering isnot more than 42 ppm (Examples 8 to 11 and Reference Example 3), thebending strength is a sufficiently large 9.7 kgf/mm² to 20.2 kgf/mm² andthe core loss is also a sufficiently low 368 kW/m³ to 433 kW/m³. Amongthese, Examples 8 to 11 were well balanced in bending strength and coreloss. Note that it was confirmed that when the amount of carbon aftersintering is 9.8 ppm (Reference Example 3), the core loss tends tobecome somewhat greater, but this is not that much of a problem inpractice.

EXAMPLES 12 to 16, REFERENCE EXAMPLE 4, AND REFERENCE EXAMPLE 5

[0101] The same procedure was followed as in Examples 1 to 7 to obtaintoroidal shaped articles and rod shaped articles except for using 49.5mol % of Fe₂O₃, 9 mol % of NiO, 10 mol % of CuO, and 31.5 mol % of ZnOas materials.

[0102] Next, the shaped articles were placed in the sintering furnacefor sintering. The sintering was performed by blowing air into thefurnace while changing the flow rate of blowing as shown in Table 3(unit:ml/min) in an air atmosphere at a sintering temperature of 1100°C. and a sintering time of 2 hours to obtain ferrite sintered bodies.

[0103] The amount of carbon of each ferrite sintered body found in thisway was measured in the same way as in Examples 1 to 7. The results areshown in Table 3.

[0104] Further, the magnetic permeability μ of each obtained ferritesintered body was measured in the same way as in Examples 1 to 7. Theresults are shown in Table 3. The relationship with the amount of carbonis shown in FIG. 6.

[0105] Further, the bending strength was tested in the same way as inExamples 1 to 7 using the rod-shaped ferrite sintered bodies. Theresults are shown in Table 3. The relationship with the amount of carbonis shown in FIG. 6. TABLE 3 Gas flow Am't of Bending Magnetic ratecarbon strength permeability (ml/min) (ppm) (kgf/mm²) μ Ref. 100 67 7.1872 Ex. 4 Ex. 12 200 58 8.3 864 Ex. 13 300 52 9 834 Ex. 14 500 36 9.9804 Ex. 15 1000 30 10.6 798 Ex. 16 3000 18.6 11.6 778 Ref. 5000 9.7 13.4755 Ex. 5

[0106] From the above results, it was confirmed that if the amount ofcarbon after sintering is 67 ppm (Reference Example 4), the bendingstrength is a relatively low 7.1 kgf/mm².

[0107] As opposed to this, when the amount of carbon after sintering isnot more than 58 ppm (Examples 12 to 16 and Reference Example 5), thebending strength is a sufficiently large 8.3 kgf/mm² to 13.4 kgf/mm² andthe magnetic permeability μ is a sufficiently large 755 to 864. Amongthese, Examples 14 to 16 were well balanced in the bending strength andmagnetic permeability. Note that when the amount of carbon aftersintering is 9.7 ppm (Reference Example 5), it was confirmed that whilethe magnetic permeability tends to fall somewhat, there is not that muchof a problem in practice.

[0108] Note that above the explanation was made of embodiments andexamples of the present invention, but the invention is not limited tothese embodiments or examples in any way. It is of course possible towork the invention in various ways within the range of the gist of theinvention.

1. A magnetic ferrite composition including at least one of Mg, Ni, Cu,Zn, Mn, and Li and having a content of carbon of less than 96 weightppm.
 2. The ferrite composition as set forth in claim 1, wherein saidferrite composition includes at least one of Cu, Zn, Mn, Ni, and Li inaddition to Mg.
 3. The ferrite composition as set forth in claim 1,wherein the content of the carbon is more than 9.7 weight ppm.
 4. Theferrite composition as set forth in claim 2, wherein the content of thecarbon is more than 9.7 weight ppm.
 5. The ferrite composition as setforth in claim 1, wherein the content of the carbon is not more than 70weight ppm.
 6. The ferrite composition as set forth in claim 2, whereinthe content of the carbon is not more than 70 weight ppm.
 7. The ferritecomposition as set forth in claim 3, wherein the content of the carbonis not more than 70 weight ppm.
 8. The ferrite composition as set forthin claim 4, wherein the content of the carbon is not more than 70 weightppm.
 9. The ferrite composition as set forth in claim 1, wherein theferrite composition includes at least Mn and Zn and the content ofcarbon is less than 52 weight ppm.
 10. The ferrite composition as setforth in claim 9, wherein the content of the carbon is more than 9.8weight ppm.
 11. The ferrite composition as set forth in claim 9, whereinthe content of the carbon is not more than 45 weight ppm.
 12. Theferrite composition as set forth in claim 10, wherein the content of thecarbon is not more than 45 weight ppm.
 13. The ferrite composition asset forth in claim 9, wherein the ferrite composition further includesas an addition component at least one kind of oxide selected fromsilicon oxide, calcium oxide, tin oxide, titanium oxide, niobium oxide,zirconium oxide, vanadium oxide, molybdenum oxide, bismuth oxide, andtantalum oxide.
 14. The ferrite composition as set forth in claim 10,wherein the ferrite composition further includes as an additioncomponent at least one kind of oxide selected from silicon oxide,calcium oxide, tin oxide, titanium oxide, niobium oxide, zirconiumoxide, vanadium oxide, molybdenum oxide, bismuth oxide, and tantalumoxide.
 15. The ferrite composition as set forth in claim 11, wherein theferrite composition further includes as an addition component at leastone kind of oxide selected from silicon oxide, calcium oxide, tin oxide,titanium oxide, niobium oxide, zirconium oxide, vanadium oxide,molybdenum oxide, bismuth oxide, and tantalum oxide.
 16. The ferritecomposition as set forth in claim 12, wherein the ferrite compositionfurther includes as an addition component at least one kind of oxideselected from silicon oxide, calcium oxide, tin oxide, titanium oxide,niobium oxide, zirconium oxide, vanadium oxide, molybdenum oxide,bismuth oxide, and tantalum oxide.
 17. The ferrite composition as setforth in claim 1, wherein said ferrite composition includes, in additionto Ni, at least one of Cu, Zn, and Mn and the content of carbon is lessthan 67 weight ppm.
 18. The ferrite composition as set forth in claim17, wherein the content of the carbon is more than 9.7 weight ppm. 19.The ferrite composition as set forth in claim 17, wherein the content ofthe carbon is not more than 60 weight ppm.
 20. The ferrite compositionas set forth in claim 18, wherein the content of the carbon is not morethan 60 weight ppm.
 21. A process of producing a magnetic ferritecomposition controling a flow rate of gas blown into a sintering furnaceso as to control an amount of carbon contained in the magnetic ferritecomposition.
 22. A method of adjusting the bending strength of amagnetic ferrite composition controling a content of carbon contained inthe magnetic ferrite composition.
 23. An electronic component having amagnetic ferrite composition including at least one of Mg, Ni, Cu, Zn,Mn, and Li and having a content of carbon of less than 96 weight ppm.